Chemical warfare agents (CWAs) present an obstacle to both the world's militaries and civilian populations. Of particular concern are those agents with both high human toxicity and long persistence. Persistence refers to the capacity of an agent to remain active and thus deny access to an area for an extended period of time. One example of such an agent is the nerve agent O-ethyl-S-(2-diisopropylaminoethyl) methylphosphonothiolate, frequently referred to as VX. Persistent chemical warfare agents, such as VX, may make an area unsafe for traversal for a considerable period of time following application of the agent. Consequently, there is exists a need in both the military and civilian populations to detect the presence of these agents in rural and urban terrains, and likewise, to demonstrate when a particular area is safe for soldiers, civilians and livestock to return safely.
The very same mechanism responsible for an agent's persistence, i.e., low vapor pressure, also makes these persistent agents difficult to detect with traditional vapor-based standoff detectors. Vapors only evolve at low rates unless the agent and the supporting matrix (soil, etc) are heated. Consequently, traditional detection mechanisms that offer high sensitivity have often required physical removal of a sample to an offsite laboratory for extraction and subsequent analysis. This manner of survey is undesirable for most military applications given that the time to collect a sample and transport the sample offsite is incompatible with the desired pace of operations. Other detection mechanisms designed to provide near real-time analysis often typically require some direct mechanical contact with the terrain. Some examples are surface wipes used with ion mobility spectrometers, chemical conversion schemes, and the membrane probe (U.S. Pat. No. 4,433,982) and contact wheel approach (U.S. Pat. No. 5,437,203) developed by Bruker. Direct contact is undesirable because components that touch the surface can become contaminated and therefore dangerous. The latter is of particular concern for any apparatus making contact with persistent agents, such as VX. The contacting surfaces can become so heavily contaminated that these surfaces are difficult or dangerous to clean and require disposal. Similarly, contamination with interferents may also mandate replacement or cleaning.
Like chemical warfare agents, unidentified energetic devices, including land mines, improvised explosive devices, and various unexploded ordinance, present a further obstacle to both the world's militaries and civilian populations.
In more privatized applications, such as law enforcement, there is a further need to understand the presence of various drug agents. In other instances, there is a need to identify the presence of certain toxic materials. One non-contact technique that has been utilized in the detection of such substances, as described herein, is through the use of ground penetrating radar, using a wideband antenna to irradiate the soil with an electromagnetic field covering a large frequency range. Reflections from the soil caused by dielectric variations are measured and are then converted into an image. This technique, however, has limitations. For example, the resolution required to image small objects requires GHz frequencies, which decrease soil penetration and increase image clutter. In addition, these systems are extremely expensive and inhibit widespread applications, such as for portable usage. Another non-contact technique, such as described in U.S. Pat. No. 6,895,804 to Lovell et al., involves the use of a strobe or laser that radiates high energy radiation in order to produce volatilization of the agents to be detected in extremely short bursts, ranging from 0.001 to 0.01 seconds in duration. These agents are then detected, using a mass spectrometer or other similar device.
In spite of the efficacy of the latter technique to detect materials of interest, there are subsidiary problems associated with its use. For example, the amount of energy required to sufficiently irradiate one particular surface—such as frozen soil—using the Lovell device could potentially cause burning of another surface, such as sod, causing damage to the collection/detection equipment, as well as to the surface. Lovell provides no mechanism to automatically compensate for the different power levels required by different surface conditions. It will be appreciated that in military or covert applications, burning or combustion of an irradiated surface can further lead to premature discovery of such detection events.
There is a need to develop a system that is capable of liberating a target analyte from soil and other diverse matrices, while simultaneously avoiding “overcooking” of the matrices. Overcooking in this sense liberates tars and other materials that are highly detrimental to virtually any type of downstream sensor.